This PDF file contains the front matter associated with SPIE Proceedings Volume 11962 including the Title Page, Copyright information, and Table of Contents.

Scleral collagen crosslinking (SCXL) to mechanically reinforce the scleral tissue and modify axial length is the most promising novel technique to treat Myopia. In this study, we use Optical coherence elastography (OCE) and mechanical testing to evaluate the impact of SCXL on different posterior scleral locations, by quantifying the shear and Young’s modulus, to characterize the biomechanical properties of posterior sclera that are better suited for a higher impact of the SCXL. 15 porcine eyes were treated with riboflavin-ultraviolet-A irradiation (UVX-SCXL). Rayleigh-wave speed was measured: (1) before treatment, (2) after 30 minutes soaking on riboflavin, (3) after UVX-SCXL treatment, and (4) after treatment in a non-treated area. Uniaxial tensile tests were performed on scleral strips. Shear and Young modulus were obtained for all conditions. Mean wave speed (WS) and shear modulus (G) for posterior sclera differed statistically for the different locations, being the POST-POST higher than POST-ANT, both in temporal (WS 85% and G ↑124%, p<0.05) and nasal (WS ↑124%, p<0.01 and G ↑160%, p<0.01) positions. UVX-SCXL treatment changed significantly the mechanical properties of posterior sclera, with higher changes induced at the most posterior locations (POST-ANT WS= 22.95±1.15 (m/s) T↑130% N↑146% and POST-POST WS= 26.28±1.41 (m/s) T↑142% N↑132%, p<0.01, averaged across frequencies)). Both shear and Young’s modulus significantly increased after treatment (averaged across eyes: G T↑249% N↑193% and E T↑320% N↑208%, p<0.01). OCE is a noninvasive, high-resolution tool to evaluate the impact of SCXL ex vivo, and in vivo in the future. Differences in posterior scleral properties should be considered to maximize the impact of UVX-SCXL treatment. UVX-SCXL in porcine scleras changes significantly the biomechanical properties and strengthen the scleral tissue. Future work will consist on the evaluation of the biomechanical and microstructural changes in posterior sclera following SCXL in myopic eyes.

The aim of this study is to compare the results of tissue stiffness estimates given by compression (strain) ultrasound elastography (S-USE) and compression optical coherence elastography (C-OCE) beyond the difference in resolution and penetration depth. Namely, the focus of this work is on the contribution of elastic nonlinearity and mechanical inhomogeneity of the tissues to the stiffness estimates and resultant diagnostic performance of these techniques. We demonstrate that in comparison with S-USE despite basically the same compression principle, the applied realization of quantitative C-OCE have novel capabilities due to its ability to obtain spatially-resolved local pressure control and the local stress-strain curve mapping within the tissue.

Mechanical properties of tissues are an important indicator because they are associated with disease states. One of the common excitation sources in optical coherence elastography (OCE) to determine mechanical properties is acoustic radiation force (ARF). Using ARF as an excitation source requires a complicated focusing alignment, that potentially increases the difficulty for translational applications. Additionally, for tissue engineering applications, samples are usually cultured in a 35 mm Petri dish or 6-well cell culture plate. As the samples placed in a such limited space and with polystyrene material, using ARF as the excitation source could generate undesired reflected waves from rigid boundaries which affect the evaluation of mechanical properties, and acoustic energy for the ARF generation could be attenuated by the bottom of the plate. Here, we reported a new technique to evaluate the mechanical property of samples placed in 6- well cell culture plate without contacting the sample, named harmonic oscillation OCE. A homogeneous 5% gelatin phantom was fabricated and placed in a 6-well cell culture plate. The actuator was driven by a 300 Hz signal with a 15- cycle burst to vibrate the plate. The spectral domain optical coherence tomography (OCT) system was used to make measurements with 100 μm lateral spacing and 3.5 μm axial resolution within 10 mm × 10 mm field of view (FOV). An 8-angle directional filter and low pass filter were used to decompose two-dimensional (2D) wave propagations and undesired frequency components, respectively. The 2D wave velocities in each direction were separately evaluated by a 2D local wave velocity algorithm. The experimental results demonstrated that the averaged 2D wave velocity represents a good agreement with the dispersion analysis via the ARF excitation. The proposed harmonic oscillation OCE with an easy-to-setup approach can be used to evaluate 2D mechanical properties of samples placed in the 6-well cell culture plate without tedious focusing alignment or directly contacting samples, which provides largely potential applications for histopathological and tissue engineering communities.

We present a new approach to Micropipette Aspiration (MPA), a pioneering method in mechanobiology, that introduces an all-optical readout to retrieve both applied stress and material response. Our technique, i.e. Hydraulic Force Spectroscopy, expands on the current MPA experimental possibilities, allowing for frequency-dependent complex moduli measurements of soft suspended bodies over a large bandwidth, with nanometric resolution. This is achieved by oscillating the pressure on the sample by tens of Pascals with a multifrequency signal, by means of a fast pump. Our goal is to use this technique to define new label-free biomarkers for different applications, e.g. embryo viability control.

The capabilities of Brillouin spectroscopy for the characterization of xenogeneic collagen-containing biomaterials have been demonstrated using a valve-containing bovine jugular vein as an example. The study of both hydrated and dried tissues taken from various animals made it possible to reveal the effects of the individual specificity and the measurement protocol for the Brillouin spectrum. It was found that the Brillouin spectrum of the dried tissue distinguishes the contributions from collagen and elastin fibers, and lipid deposits located mainly on the outer side of the vein.

The biomechanical properties of the crystalline lens play a critical role in eye health and vision. In this study, we used focused acoustic radiation force (ARF) to induce surface waves in young and mature rabbit lenses in situ and to measure the viscoelastic properties of the lenses inside the eyeball. Phase-sensitive optical coherence elastography (OCE) system was used to image the wave propagation, and the wave dispersion was quantified by spectral analysis. The results show that the dispersion of the ARF-induced elastic waves was different between the young (N=5) and mature (N=10) lenses. Young’s modulus and shear viscosity coefficient were quantified based on a Scholte wave model. The results show that both elasticity and viscosity are significantly different between the young and mature lenses. The Young’s modulus of the lenses increased with age from 7.74±1.56 kPa (young) to 15.15±4.52 kPa (mature), and the shear viscosity coefficient increased from 0.55±0.04 Pa·s (young) to 0.86±0.13 Pa·s (mature). In conclusion, the combination of ARF excitation, OCE imaging, and dispersion analysis enabled non-invasive quantification of lenticular viscoelasticity in situ.

The crystalline lens is enclosed in a membrane, which presses upon the lens molding it into the required shape to enable dynamic focusing of light. Yet, the effect of the capsule membrane characteristics on the lens biomechanical properties has not been fully investigated. In this study, the lens viscoelasticity was assessed using phase-sensitive spectral-domain optical coherence tomography (PhS-OCT) coupled with acoustic radiation force (ARF) excitation before and after the capsular bag was dissected away. The ARF excitation was focused on the anterior pole of the lens, and two orthogonal MB mode scans were performed for each lens sample before and after removal of the lens capsule. The resulting elastic wave group velocity, 𝑉, in the lens with capsule intact (𝑉 = 2.60 ± 0.21 𝑚/𝑠) was found to be significantly higher (p < .001) than after the capsule was removed (𝑉 = 1.14 ± 0.15 𝑚/𝑠). Similarly, the viscoelastic assessment using surface wave dispersion model showed that both the Young’s modulus and shear viscosity of the encapsulated lens (𝐸 = 8.14 ± 1.10 𝑘𝑃𝑎, 𝜂 = 0.89 ±0.093 𝑃𝑎 ∙ 𝑠) was significantly higher than that of the decapsulated lens (𝐸 = 3.10± 0.43 𝑘𝑃𝑎, 𝜂 = 0.28 ±0.021 𝑃𝑎 ∙ 𝑠). These findings, together with the geometric differences between encapsulated and decapsulated lens as quantified from structural OCT images, indicate that the capsule is a key lenticular component that determines the stiffness and structural integrity of the lens.